Oncogenes appear to play important roles in the processes of cellular proliferation and differentiation. Technical problems have limited the study of their expression by normal myeloid cells. The techniques of in situ hybridization allow the analysis of gene expression by individual cells. We propose to apply the techniques of in situ hybridization to normal and leukemic myeloid cells. This will permit comparison of the expression of oncogenes by normal myeloid cells with the expression by leukemic cells, and a correlation of leukemic oncogene expression with their morphologic, histochemical, and chromosomal characteristics. A cDNA library for myeloid cell differentiation will be created and from this library a gene whose expression is increased, and a gene whose expression is decrease during myeloid differentiation will be cloned. These genes will be characterized and sequenced, and the amino acid sequence and control regions will be compared to those of other known proteins. These genes will be used to create probes for in situ hybridization, and the expression of these genes by normal myeloid and leukemic cells will be studied.